The present invention relates to a pressure-responsive surgical tool assembly, and more particularly, concerns a surgical retractor tool which provides an indication of the pressure being applied by the retractor against tissue or the like during surgery.
During surgical operations, a retractor is employed to expose the area on which the operation is contemplated; the retractor's purpose is to separate the edges of a surgical incision and then restrain the underlying tissues or organs from interfering with the operative process. Most retractors are hand-held by the surgeon who manipulates the retractor until the area to be worked on is properly exposed. Once the retractor is properly in position, it is often mounted in suitable framework in order to maintain that position and prevent the retractor from inadvertent movement.
Use of a retraction instrument during surgery of course necessitates caution when pressing the retractor blade against tissue, an organ or the like; extreme care is taken so that damage to the retracted item may be avoided. In most cases, the surgeon can visualize the retracted tissue clearly enough to determine that the retractive movements are not causing any harm to the patient. However, there are instances during surgery when the manipulation of the retractor may be causing damage to the tissue or organ unbeknownst to the surgeon due to the delicacy of the organ or lack of sufficient feedback data to indicate to the surgeon that excessive pressure by the retractor is occurring. These conditions arise, for example, during brain surgery wherein the retractor is utilized to hold back sections of the dura covering the brain or even portions of the brain itself. Inasmuch as the brain is very sensitive to application of pressure, use of the retractor in this area of the body could cause problems if not closely monitored. For instance, excessive pressure against the brain during craniotomies by a brain retractor have been known to cause significant edema in the area corresponding to retractor blade location. Excessive pressure by the brain retractor for protracted periods could even cause functional neurobiological changes in the patient. One reason for undue application of excessive pressure by the brain retractor is that the amount of pressure of the hand-held retractor against the brain tissue is based purely on the skill and judgment of the surgeon. Another explanation is that retraction pressure is generally excessive when that pressure surpasses local venous pressure in vessels within the retracted area, such that local blood flow is restricted or occluded. The relationship of hand-held retraction pressure to venous pressure is virtually indeterminable without some means of measurement. The surgeon's experience, skill and understanding of the operation are factors which dictate the utilization of the brain retractor and the pressure which is applied thereby, including the length of time the retractor is applied. In other words, the surgeon who uses this commonly employed hand-held brain retractor has had no real, monitored indication of the amount of pressure which is being applied against the brain surface during this surgery. As a result, reliance upon the "feel" of the surgeon could cause inadvertently high pressure being applied which, in the long run, may restrict or occlude blood flow and actually cause serious defects in the brain's function. It can be seen that there is a real and serious need to provide the surgeon with a retraction device for brain surgery and other delicate surgical operations which will allow him to monitor or even regulate the amount of pressure being applied by the retraction device.
There have been other devices used to assist medical staff in acquiring data particularly about the brain. For example, it has been known to monitor intracranial pressure to quickly locate areas of elevated pressure which may stem from a variety of different causes. One such device, commonly referred to as the "Numoto" switch is described in U.S. Pat. No. 3,649,948. This Numoto-type switch is implanted within the skull of a patient to monitor intracranial pressure. The switch, which is generally flat and may be the size of a dime, consists of two contact electrodes sealed in a thin silicone rubber envelope and connected to an external manometer reservoir by a pneumatic tube. Pressure within the cranium is registered on the manometer. However, neither the Numoto-type switch described in the above patent nor other devices available to the surgeon have been employed in the sense of a retraction instrument in order to provide a surgeon with actual pressure data during the operation itself when the retraction instrument is being utilized to hold back tissue, organs, and sensitive areas of the body. Accordingly, in order to provide the surgeon with such a retraction device for indicating pressure levels applied by the retractor, the present invention is directed.